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Control plant bugs, thrips in cotton

Scout and spray: That’s how Mid-South cotton growers effectively manage plant bugs, says Scott Stewart, University of Tennessee entomologist. “With rare exceptions, we recommend that anyone growing cotton use an independent crop consultant to scout the crop. When economic thresholds are reached, spray timely — and use the right materials.”

Stewart says his Tier 1 products for plant bug control are Transform (which is used under a Section 18), Orthene, Diamond, and Bidrin. He recommends using Diamond at least once during a season, typically around bloom, plus or minus a week, because it is a different mode of action than everything else.

“This insect growth regulator does a good job of controlling immature plant bugs,” he says. “We often tank mix it with Orthene, Bidrin, or Centric, since Diamond doesn’t control adult plant bugs. In the Mid-South, we have some concerns about development of resistance to neonicotinoids like Centric and imidacloprid, which we’ve been relying on for early-season control of adults.

Even though 2017 was a relatively light plant bug year for the Mid-South, several of Stewart’s field trials that weren’t treated for plant bugs lost well over a bale of cotton per acre.

“Where we didn’t control plant bugs, many of my trials dropped from 3,500 to 3,800 pounds of seed cotton to 1,700-2,500 pounds of seed cotton,” he says. “Failure to manage plant bugs in higher pressure situations can result in a loss of 400 to 500 pounds of lint.”

The good news is that a couple of well-timed insecticide application made all the difference.

Plant bugs can be a pest beginning at pinhead square, on through cut-out. Stewart, who is a member of the Mid-South Entomologist Working Group, recommends using a sweep net the first couple weeks of squaring, and treating with counts of 8 per 100 sweeps. Afterward, the threshold goes up to 15 bugs per 100 sweeps.

“Once the crop gets very far into bloom, we recommend switching to a drop cloth, which is more accurate than sweeps in sampling nymphs,” he says. “With the shake cloth, we recommend treating with counts of three or more plant bugs per drop cloth until the crop is no longer susceptible.”

SOUTHWEST COTTON

Thrips remain the top early-season pest in west Texas cotton, says Kerry Siders, Texas A&M AgriLife Extension IPM agent. More thrips pressure occurs farther north and west of Lubbock, where more wheat is produced.

“Our area has been extremely dry for about four months,” Siders says. “The dry weather has taken a toll on the wheat that we use primarily for a cover crop, planted on turnrows, and sometimes in the field. Wheat and weeds act as a host crop for thrips before we plant cotton. Right now, it is so dry that thrips pressure might not be as much as in previous years. However, we need to be prepared because thrips move around and can infest fields.”

Cotton can be protected with an insecticide seed treatment, an in-furrow application, and/or a foliar spray. Instead of investing in prophylactic protection from a seed treatment or an in-furrow application, some growers rely on foliar applications of a material like Orthene, Bidrin, or dimethoate; this strategy can initially save a grower money, but can cost him time — and yield.

“Untreated, a heavy thrips infestation can easily delay the crop up to 14 days,” Siders says. “And trying to manage thrips by relying strictly on spraying foliage can cost you up to a week in crop maturity, because you have already sustained some damage by the time you notice you have thrips. A delay in maturity can make a huge difference in earliness.

“So, being proactive and managing thrips prophylactically is a better strategy because the crop doesn’t sustain injury and lose earliness. We recommend using a seed treatment or an in-furrow application. These fairly affordable treatments also provide protection from other minor pests.

“Seed treatments include Gaucho, Aeris, Avicta Elite, or acephate; and in-furrow treatments include Velum, Admire Pro, and Orthene. I would use Velum where I had a history of nematodes and thrips.”

SOUTHEAST COTTON

The most predictable insect pest of cotton in the Southeast continues to be tobacco thrips, and thrips are certainly the most important group of insects on seedling cotton in the region, says Jeremy Greene, Clemson University entomologist.

“Despite mounting evidence that tobacco thrips are developing resistance to the neonicotinoid insecticides, seed treatments containing neonicotinoids remain the most common at-plant strategy for addressing thrips in cotton,” he says.

“In many cases, the approach is still effective, but control doesn’t last as long as it used to. As in other regions of the country, other preventative insecticides are also put in the furrow as a granular material, such as AgLogic, with activity on thrips and nematodes, or Thimet, with activity on thrips only, or an in-furrow liquid spray, such as Admire Pro (thrips only), Velum Total (thrips plus nematodes), or Orthene (thrips only).”

Southeast cotton occasionally experiences an aphid situation that can impact yield, especially in drought-stress conditions in young dryland cotton, Greene says. “However, aphids usually are not a huge economic pest in Southeast cotton. We also sometimes have outbreaks of spider mites and plant bugs in isolated situations.

“In the Southeast, plant bugs historically have not been an issue in cotton. We do have to address them in certain fields, but it is more a one-shot situation instead of multiple sprays. Recently, there have been more reports of plant bug issues, particularly in North Carolina and Virginia. Additionally, portions of Alabama have plant bug issues more similar to those in the Mid-South.”

FAR WEST

Cotton insect management, in Arizona in particular, depends on a fully developed integrated pest management program. Like almost anywhere else, this program depends on regular sampling and effective use of insecticides.

“However, things here are a little different after that,” according to Peter Ellsworth, University of Arizona entomologist and IPM specialist. “Our IPM program really depends on the natural controls provided by a large suite of generalist predators — and our sometimes harsh weather.”

Lygus bugs are the No. 1 yield-limiting pest, and whiteflies are the No. 1 quality-limiting pest. But both are scouted carefully, the former with a sweep net and the latter with direct counts of adults on leaves and of immobile large nymphs on quarter-sized leaf disks. Whether it is lygus or whiteflies, pest control advisors look to spray only materials that are fully safe to the beneficial insect complex that is present.

New research points to ways that PCAs can count one or more of six species of generalist predators as a way to further adjust thresholds for spraying. These include big-eyed bug, Geocoris pallens; minute pirate bug, Orius tristicolor; crab spider, Misumenops celer; Drapetis dance flies; Collops beetles; and lacewing larvae.

These bulwarks of the Arizona IPM plan are supported and conserved by the use of insecticides that selectively target either lygus bugs or whiteflies. Arizona uses either Carbine or Transform in rotation to control lygus; both are safe on beneficials. And, they usually spray Courier, Knack, or Oberon to control whiteflies as options that are safe to natural enemies.